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By Doug71
I have been asked to make an oak bookcase by a local kitchen company, it is about 1070mm high, 1400 long and around 220 deep. It will be made out of 40mm oak worktop which they are supplying and probably an oak veneered ply back, very simple/plain modern design.

The problem is caused by the position of it, it is kind of half sunk in to the other units/worktop (granite), it looks on to the dining room and the sink is behind it. The unit stands 170mm above the worktop so creates a kind of splashback/upstand behind the sink, because of this the top back of unit will be seen and have a clear glass splashback fitted to it.

Because the back of the unit needs to finish flush with no visible fixings I was going to rebate the ply back to fit in a groove around the inside of the top and sides.

My concern is wood movement, if the top and shelves shrink in length at all the sides can't move because of the ply back. I know wood doesn't move much in length, am I really over thinking this and worrying about nothing?

I know an image would make it easier but don't know how yet.

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By AndyT
I've not done kitchens but I've made a few bookcases. As far as my understanding goes, any variation in the length of the shelves will be minimal, and so would any variation in the width of the ply back, so ignorable in practice. I've always ignored it. :)
If you are still worried, you could just make the rebate a mm or so wider than the ply back. Use thin pins to fix the back in place and they can bend a little if they ever need to.
By profchris
Along the grain - minimal movement.

I'd be more concerned about cupping or twist in the sides, shelves and top, because oak does move more than most with humidity. Is the worktop material laminated from strips? That cuts down the risk because movement in each part tends to cancel out. I'd check the end grain - that will tell you how each strip will want to move.
By Just4Fun
profchris wrote:I'd be more concerned about cupping or twist in the sides, shelves and top, because oak does move more than most with humidity.

I didn't know that. I made a set of shelves for my kitchen. Verticals are pine and horizontals are oak. It holds tea, coffee, tea pots and such like so I have it on the wall above where the kettle sits on a worktop. I expected humidity to cause a problem due to the steam from the kettle rising onto the shelves, but went ahead anyway. It has been there for a year so far with no sign of problems.
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By MikeG.
As long as you house out properly for the shelves they won't cup. If the outside of the verticals aren't on show (ie hidden by other stuff) you can put a couple of longitudinal relieving cuts along them, and that will stop them cupping too. Otherwise, if you are really concerned with cupping (I'm not sure I'd worry), then you might screw through the verticals into the end of the shelves, and pellet the heads. Don't worry about shrinkage. That only happens across the grain (to the extent that it would ever cause issues), not along it. All your grain directions are going to be aligned, so there is no problem.

Frankly, in this situation I'd be much more concerned with the finish (if it is forming part of the splashback) than I would with timber movement.
By Doug71
Thanks for the replies, guess I was overthinking as always.

The worktops it's made from will be the prime oak ones from worktop express so hoping there won't be much if any cupping.

Mike, the shelves won't be housed in but will have some big dominos in the end, I will also be screwing through the sides as most of it will be hidden, will plug the ones that are not hidden.

Regards finish I am avoiding that one, there is a big oak topped island with an under mount sink in which will need well sealing so presume the bookshelf will be finished to match. Like I said it will have a glass splash back fitted to the back which should protect it.

Thanks again, Doug
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By MikeG.
I just don't understand this. You're worried about wood moving, but choose dominoes rather than a simple stopped housing.

At least if the sides are hidden you can run a couple of relieving cuts along those, as I said.